case of the nonexistent brain

No, the title doesn't refer to a particularly vicious insult. It refers to a misleading story I've received numerous times via email. To summarize, a teacher/professor tells a student that since God can't be directly observed God must not exist. Then the student retorts that since the teacher/professor's brain can't be directly observed his/her brain must not exist, either. Not nearly as poetic as comparing God to the wind, but much more incisive. (It also superficially resembles another gambit: if all human thoughts originate from lumps of matter called "brains", then how can someone trust any of his or her own conclusions?)

The story's moral is certainly valid: not everything that exists can be directly sensed. However, any readers of the story (and there are many) should not be misled into applying this childish moral to the actual philosophical clash between belief systems that include the supernatural and belief systems that deny it. The problem isn't that the moral is inapplicable to the clash; the problem is that the moral offers no "ammunition" for either side, because everybody believes it. To represent the opposing point of view as being so crippled is dishonest.

In fact, very few human endeavors of significance can happen without assuming the truth of this moral. When someone shakes a closed, opaque container or weighs it to determine how much is inside the container, the inability to directly sense the contents doesn't result in someone assuming the contents don't exist. When a hurtling object is momentarily blocked from view by a tree or pole, the inability to directly sense the object for an instant doesn't result in someone assuming the object blinked out of existence. The inability to see germs or atoms with the unaided eye doesn't result in someone assuming such things don't exist. The inability to directly sense thermodynamic energy (we only see evidence of energy when it's transferred by doing something) doesn't result in someone assuming it spontaneously appears and vanishes.

Unlike the teacher caricature in the story, people who say there's no proof for the supernatural can then say they have brains without contradicting themselves. They would do this by patiently enumerating the "brain evidence": over time many observations have consistently shown that humans have brains, and over time many other observations have consistently shown that the body under consideration, exhibit "Me", is indeed a human just like the rest. Therefore, it's reasonable to conclude that exhibit "Me" has a brain. They would then go on to state that a similar chain of evidence doesn't hold for evaluating statements about the supernatural.

One last important point is that the moral doesn't act as a persuasive point for the existence of any given supernatural entity. In short, the truth that some things that exist are nonphysical does not mean that anything that is nonphysical exists. Don't accidentally place God in the same category as leprechauns and fairies.